The present invention relates to a physical or dynamic quantity detecting apparatus and a sensor failure or abnormality detecting system incorporated in this apparatus.
A conventional pressure sensor comprises a semiconductor substrate with a thin diaphragm portion. Two pressure detecting elements (i. e., gauge resistors) are formed in a central region of this diaphragm portion, and another two pressure detecting elements are formed in a peripheral portion of this diaphragm portion. These four pressure detecting elements are arranged to form a Wheatstone""s bridge circuit. When a pressure is applied on the diaphragm portion, the resistance of each pressure detecting element varies due to a piezoresistance effect. A significant difference (i.e., an output voltage) appears between a midpoint of the pressure detecting elements in the central region and a midpoint of the pressure detecting elements in the peripheral region. The pressure sensor amplifies and adjusts this output voltage appropriately to produce an electric signal representing the pressure applied on the diaphragm portion.
As described above, the pressure sensor amplifies and adjusts a voltage difference produced from the bridge circuit. However, the bridge circuit produces an erroneous voltage difference when spoiled or wounded. In such a case, the pressure sensor produces an erroneous electric signal.
The PCT application WO97/05464 discloses a pressure sensor having a failure detecting capability. According to this prior art, the pressure sensor detects an abnormal distribution of the stress in the diaphragm portion. To this end, the diaphragm portion is separated into two regions at the center. A bridge circuit is formed in each region. A sensor failure is detectable based on a deviation in the output voltage of respective bridge circuits. However, this pressure sensor is not desirable in that the area of pressure sensing portion is doubled due to separation of the diaphragm portion along the center line. Thus, downsizing of the pressure sensor is difficult.
Another conventional pressure sensor includes a sensor chip adhered on a pedestal by an anode bonding so as to form a reference pressure chamber. The pressure detection is performed based on a pressure difference between an external pressure and the reference pressure. In general, adhering of the sensor chip onto the pedestal is performed in a vacuum to avoid oxidation of aluminum wiring formed on the sensor chip. Thus, the reference pressure chamber is maintained in a vacuum condition (i.e., 0 atm absolute).
When this pressure sensor is subjected to an extremely high pressure (for example, in the detection of a hydraulic braking pressure), it is necessary to match the voltage range of a sensor output with the measuring pressure varying in a wide zone. Thus, the sensitivity of the pressure sensor must be suppressed to a low level.
This makes it difficult to detect a sensor failure by solely monitoring the sensor output.
Furthermore, when the sensor chip peeled off the pedestal, the reference pressure chamber communicates with an external atmosphere. Thus, the reference pressure becomes equal to the external pressure. However, when the same pressure is detected as two series of signals like the above-described failure detecting method, a similar situation possibly appear when these signals are compared mutually. Hence, it is impossible to accurately detect the sensor failure.
In view of the above-described problems, the present invention has an object to provide a pressure sensor which is surely capable of detecting a sensor failure when the resistance value in a bridge circuit has varied due to trouble or damage.
Furthermore, the present invention has another object to provide a pressure sensor which is preferable in downsizing of the pressure sensor.
Moreover, the present invention has another object to provide a pressure sensor which is capable of detecting a sensor failure caused by a defective airtightness of the reference pressure chamber formed by adhering a sensor chip on a pedestal.
To accomplish the above and other related objects, the present invention provides a first pressure sensor comprising a semiconductor substrate having a diaphragm portion, a pressure detecting bridge circuit comprising gauge resistors having resistance values varying in response to a pressure applied on the diaphragm portion of the semiconductor substrate, and a reference voltage generating circuit connected between one end and the other end of the pressure detecting bridge circuit for generating a reference voltage, the reference voltage generating circuit comprising non-sensitive resistors having resistance values not varying in response to the pressure applied on the diaphragm portion. A failure judgement of the pressure detecting bridge circuit is performed based on a voltage difference between two midpoints of the pressure detecting bridge circuit as well as a voltage difference between a voltage level of either of two midpoints of the pressure detecting bridge circuit and the reference voltage level of the reference voltage generating circuit.
With this arrangement, it becomes possible to surely detect a sensor failure when the resistance value of the bridge circuit is changed due to the failure.
Furthermore, it is preferable that the gauge resistors constituting the pressure detecting bridge circuit are constituted by separate gauge resistors, and a failure judgement of the pressure detecting bridge circuit is performed based on a voltage difference between two midpoints of the pressure detecting bridge circuit as well as a voltage difference between a pair of intermediate terminals selected from intermediate terminals of the separate gauge resisters, the selected pair of intermediate terminals having the same voltage level in a condition where no pressure is applied on the diaphragm portion.
With this arrangement, it becomes possible to surely detect a sensor failure when the resistance value of the bridge circuit is changed due to the failure.
Furthermore, it is preferable that a failure judgement of the pressure detecting bridge circuit is performed based on voltage differences between one and the other terminals of the bridge circuit and first and second intermediate terminals of the bridge circuit.
With this arrangement, it becomes possible to surely detect a sensor failure when the resistance value of the bridge circuit is changed due to the failure.
Furthermore, it is desirable that an amplification circuit is provided to amplify each voltage difference, and the failure judgement of the pressure detecting bridge circuit is performed based on an output signal of the amplification circuit.
Furthermore, the present invention provides a second pressure sensor comprising a semiconductor substrate having a diaphragm portion, a pressure detecting bridge circuit for outputting an electric signal representing a pressure applied on the diaphragm portion of the semiconductor substrate, the pressure detecting bridge circuit comprising two gauge resistors provided in a first direction and two other gauge resistors provided in a second direction normal to the first direction. A failure detecting circuit, provided at a predetermined region of the diaphragm portion where the pressure detecting bridge circuit is not formed, outputs an electric signal in response to the pressure applied on the diaphragm portion. The failure detecting circuit has a sensitivity different from that of the pressure detecting bridge circuit. A failure judging means is provided for performing a failurejudgement of the pressure detecting bridge circuit based on the output signals of the pressure detecting bridge circuit and the failure detecting circuit.
In this manner, by using the output signals of the pressure detecting bridge circuit and the failure detecting circuit which have mutually different sensitivities, it becomes possible to surely detect a sensor failure when an output of the pressure detecting bridge circuit is changed due to the failure.
According to a conventional pressure sensor, the gauge resistors constituting the pressure detecting bridge circuit are disposed on the diaphragm portion along two perpendicular directions with two resistors on each direction. The remaining portion is a unused region. However, according to the above second pressure sensor of the present invention, the failure detecting circuit is provided in this unused region of the diaphragm portion. Thus, it becomes possible to provide a pressure sensor having the capability of detecting a sensor failure with a sensing portion whose size is substantially identical with that of the conventional pressure sensor. Thus, the pressure sensor can be downsized.
Furthermore, it is preferable that a memory means is provided for storing a relationship between output characteristics of the pressure detecting bridge circuit and output characteristics of the failure detecting circuit, wherein the failure judging means performs the failure judgement of the pressure detecting bridge circuit by checking at an arbitrary pressure point whether or not the output characteristics of the pressure detecting bridge circuit and the output characteristics of the failure detecting circuit satisfy the relationship stored in the memory means.
For example, the failure detecting circuit comprises at least one gauge resistor. And, the gauge resistor constitutes a failure detecting bridge circuit.
It is further preferable that the pressure detecting bridge circuit and the failure detecting circuit are constituted by diffused resistors. The pressure detecting bridge circuit can be constituted by diffused resistors and the failure detecting circuit are constituted by thin-film resistors. Furthermore, the failure detecting circuit can be constituted by a capacitive sensor.
Furthermore, the failure judging means can be provided on the semiconductor substrate on which the pressure detecting bridge circuit and the failure detecting circuit are provided.
Furthermore, the present invention provides a third pressure sensor comprising a sensor chip constituted by a semiconductor substrate with a diaphragm portion, a pedestal on which the sensor chip is adhered, and a reference pressure chamber formed between the sensor chip and the pedestal. A pressure detecting bridge circuit consisting of gauge resistors is formed on the diaphragm portion to output an electric signal representing a pressure applied on the diaphragm portion. A failure detecting bridge circuit consisting of gauge resistors is formed on a specific region of the diaphragm portion different from the pressure detecting bridge circuit. The failure detecting bridge circuit outputs an electric signal responsive to the pressure applied on the diaphragm portion. And, a sensitivity of the failure detecting bridge circuit is higher than a sensitivity of the pressure detecting bridge circuit.
In this manner, by providing a high-sensitive failure detecting bridge circuit independent of the low-sensitive pressure detecting bridge, it becomes possible to detect a sensor failure caused by a defective airtightness of the reference pressure chamber formed by adhering the sensor chip on the pedestal.
According to preferred embodiments of the present invention, the gauge resistors constituting the failure detecting bridge circuit are disposed in the vicinity of the center of the diaphragm portion and in the vicinity of a peripheral end of the diaphragm portion. The gauge resistors constituting the failure detecting bridge circuit can be disposed at a specific position of the diaphragm portion where a tensile stress is maximized and a specific position of the diaphragm portion where a compressive stress is maximized.
With this arrangement, it becomes possible to increase the sensitivity of the failure detecting bridge circuit.
According to the preferred embodiments of the present invention, the gauge resistors constituting the pressure detecting bridge circuit are disposed in the vicinity of a midpoint between the center and the peripheral end of the diaphragm portion. The gauge resistors constituting the pressure detecting bridge circuit can be disposed at a specific position of the diaphragm portion where a tensile stress is minimized and a specific position of the diaphragm portion where a compressive stress is minimized.
With this arrangement, it becomes possible to decrease the sensitivity of the pressure detecting bridge circuit.
According to the preferred embodiments of the present invention, the semiconductor substrate has a (100) surface, and the gauge resistors constituting the failure detecting bridge circuit comprise a first gauge resistor extending in a first direction and a second gauge resistor extending in a second direction normal to the first direction.
In this manner, by differentiating the longitudinal direction of the first gauge resistor from the longitudinal direction of the second gauge resistor, it becomes possible to differentiate the resistance changes of respective gauge resistors in response to a surface stress. Accordingly, even when the first gauge resistor is located adjacent to the second gauge resistor, it becomes possible to obtain electric signals responsive to the applied pressure from the first and second gauge resistors.
According to the preferred embodiments of the present invention, the failure detecting bridge circuit is constituted by a full-bridge circuit consisting of four gauge resistors. Constituting the failure detecting bridge circuit by a full-bridge circuit is effective to increase the sensitivity compared with the half-bridge circuit.
Furthermore, the present invention provides a fourth pressure sensor comprising a diaphragm portion, a reference pressure chamber isolated by the diaphragm portion, an output circuit for outputting an electric signal representing a pressure applied on the diaphragm portion by using pressure detecting elements formed on the diaphragm portion or in a peripheral region of the diaphragm portion, and judging means for detecting an abnormal situation that a reference pressure in the reference pressure chamber becomes equal to an outside pressure of the diaphragm portion.
In this manner, by detecting the abnormal situation that the pressures of both sides of the diaphragm portion becomes identical, it becomes possible to detect a sensor failure caused by a defective airtightness of the reference pressure chamber formed by adhering the sensor chip on the pedestal.
Furthermore, it is preferable that a pressure detecting circuit is provided for outputting an electric signal representing a pressure applied on the diaphragm portion by using pressure detecting elements formed on the diaphragm portion or in a peripheral region of the diaphragm portion, and a failure detecting circuit is provided for outputting an electric signal representing the pressure applied on the diaphragm portion, the failure detecting circuit having a higher sensitivity than that of the pressure detecting circuit.
In this manner, by providing a combination of a high-sensitive failure detecting circuit and a low-sensitive pressure detecting circuit, it becomes possible to detect a sensor failure caused by a defective airtightness of the reference pressure chamber formed by adhering the sensor chip on the pedestal.
In this case, it is preferable that the pressure detecting elements are gauge resistors, and the gauge resistors are disposed in such a manner that a resistance change of gauge resistors constituting the failure detecting circuit responsive to a change of the pressure applied on the diaphragm portion becomes larger than a resistance change of the pressure detecting circuit.
Furthermore, the present invention provides a failure detecting method for a pressure sensor comprising a diaphragm portion and a reference pressure chamber isolated by the diaphragm portion, the failure detecting method comprising a step of obtaining an electric output signal representing a pressure applied on the diaphragm portion by using pressure detecting elements formed on the diaphragm portion or in a peripheral region of the diaphragm portion, and a step of presuming an abnormal situation when the electric output signal indicates that a reference pressure in the reference pressure chamber becomes equal to an outside pressure of the diaphragm portion.
In this manner, by presuming an abnormal situation when the electric output signal indicates that the pressures of both sides of the diaphragm portion become identical, it becomes possible to detect a sensor failure caused by a defective airtightness of the reference pressure chamber formed by adhering the sensor chip on the pedestal.
Furthermore, the present invention has an object to provide a sensor abnormality detecting circuit which is compact in size, quick in response, and excellent in accuracy, and preferably used for a sensor having a pair of output terminals generating output voltages varying in mutually opposed positive and negative directions in response to a sensed physical quantity by the same voltage amount with respect to a predetermined equilibrium voltage.
Furthermore, the present invention has an object to provide a physical quantity detecting apparatus using the above sensor abnormality detecting circuit.
Moreover, the present invention provides a first sensor abnormality detecting circuit for a sensor having a first output terminal generating a first output voltage and a second output terminal generating a second output voltage. The first output voltage and the second output voltage vary in mutually opposed positive and negative directions in response to a sensed physical quantity by the same voltage amount with respect to a predetermined equilibrium voltage. The sensor abnormality detecting circuit comprises a reference voltage generating circuit for generating a reference voltage substantially identical with the equilibrium voltage. An operational amplifier has one input terminal receiving the reference voltage generated from the reference voltage generating circuit. A first resistor has one end receiving the first output voltage of the sensor and the other end connected to the other input terminal of the operational amplifier. A second resistor has one end receiving the second output voltage of the sensor vand the other end connected to the other input terminal of the operational amplifier. The second resistor has the same resistance value as that of the first resistor. A third resistor is connected between an output terminal of the operational amplifier and the other input terminal of the operational amplifier. And, a judging circuit for generating an abnormal signal notifying an occurrence of sensor abnormality when an output voltage of the operational amplifier is outside a predetermined normal voltage range.
In the above first sensor abnormality detecting circuit, it is now assumed that V1 represents the first output voltage, V2 represents the second output voltage, and VE represents the reference voltage. The first resistor and the second resistor have a resistance R, and the third resistor has a resistance Xxc2x7R. The output voltage VOUT of the operational amplifier is defmed by the following formula 2-1.
VOUT=xe2x88x92X{(V1xe2x88x92VE)+(V2xe2x88x92VE)}+VExe2x80x83xe2x80x83(2-1)
More specifically, a first value is obtained by subtracting the reference voltage VE from one output voltage V1 of the sensor. A second value is obtained by subtracting the reference voltage VE from the other output voltage V2 of the sensor. The first value and the second value are added. The operational amplifier produces the output voltage VOUT which is proportional to the sum of the first value and the second value.
Among the output voltages V1 and V2 of the sensor, it is assumed that the first output voltage V1 changes in the positive direction in response to an increase of the sensed physical quantity while the second output voltage V2 changes in the negative direction in response to the increase of the sensed physical quantity. Furthermore, xcex94V1xe2x80x2 represents an absolute difference (|V1xe2x88x92VE|) between the first output voltage V1 and the reference voltage VE, and xcex1V2xe2x80x2 represents an absolute difference (|V2xe2x88x92VE|) between the second output voltage V2 and the reference voltage VE. The above formula 2-1 is rewritten by the following formula 2-2.
VOUT=xe2x88x92X(xcex94V1xe2x80x2xe2x88x92xcex94V2xe2x80x2)+VExe2x80x83xe2x80x83(2-2)
Thus, the operational amplifier produces the output voltage VOUT which is proportional to the difference between xcex94V1xe2x80x2 and xcex94V2xe2x80x2.
As the reference voltage VE generated from the reference voltage generating circuit is substantially equal to the equilibrium voltage V0 of the sensor, the output voltage VOUT of the operational amplifier is substantially equal to VE when the operation of sensor is normal as understood from the formulas 2-1 and 2-2.
When the operation of sensor is abnormal, the balance of output voltages V1 and V2 is lost. More specifically, the absolute difference xcex94V1 between the first output voltage V1 and the equilibrium voltage V0 is not equal to the absolute difference xcex94V2 between the second output voltage V2 and the equilibrium voltage V0. The output voltage VouT of the operational amplifier is deviated to either a positive direction or a negative direction with respect to the reference voltage VE.
Hence, in the sensor abnormality detecting circuit, the judging circuit makes a judgement as to whether the output voltage VOUT of the operational amplifier is outside the predetermined normal voltage range. When the output voltage VouT is outside the predetermined normal voltage range, the judging circuit outputs an abnormal signal notifying an occurrence of abnormality in the sensor.
With this arrangement, the abnormality of sensor is accurately detected based on the output voltages and obtained at the same time. Furthermore, the abnormality of sensor is so quickly detectable that the delay time is substantially eliminated. It is not necessary to provide a high-performance information processing apparatus, such as MPU. Thus, it becomes possible to provide a small-scale circuit arrangement for detecting the abnormality of sensor.
In the above sensor abnormality detecting circuit, it is desirable that a first buffer is provided for receiving the first output voltage of the sensor and applying the received first output voltage to the one end of the first resistor, and a second buffer is provided for receiving the second output voltage of the sensor and applying the received second output voltage to the one end of the second resistor. Namely, the first buffer is provided between the first output terminal of the sensor and the first resistor. The second buffer is provided between the second output terminal of the sensor and the second resistor.
With this arrangement, it becomes possible to prevent the current from flowing from the output terminals of the sensor into the circuit consisting of the operational amplifier and the first to third resistors. The abnormality of sensor can be accurately detected.
Furthermore, in addition to the first buffer and the second buffer, it is preferable that a third buffer is provided for receiving the reference voltage generated from the reference voltage generating circuit and supplying the received reference voltage to the one input terminal of the operational amplifier.
The first buffer, the second buffer, and the third buffer may output a voltage identical with the input voltage. However, it is also desirable that the first buffer, the second buffer, and the third buffer are level shift circuits each shifting an input voltage by a specific voltage Vsf to generate an output voltage. In this case, the shift voltage is either a positive or a negative value. Respective buffers can be level shift circuits having the same circuit arrangement.
More specifically, when the first to third buffers are constituted by the level shift circuits, the one end of the first resistor receives avoltage (=V1+Vsf) obtained by shifting the first output voltage V1 by the voltage Vsf The one end of the second resistor receives a voltage (=V2+Vsf) obtained by shifting the second output voltage V2 by the voltage Vsf. One end input terminal of the operational amplifier receives a voltage (=VE+Vsf) obtained by shifting the reference voltage VE by the voltage Vsf Thus, all of three input voltages are equally shifted by the same voltage Vsf. Therefore, the operational amplifier produces the output voltage VOUT which is proportional to a sum of a first value obtained by subtracting the reference voltage VE from the one output voltage V1 of the sensor and a second value obtained by subtracting the reference voltage VE from the other output voltage V2 of the sensor.
In general, the level shift circuit has a simple arrangement compared with the buffer outputting a voltage identical with an input voltage. Therefore, the circuit scale of the sensor abnormality detecting circuit can be reduced.
Furthermore, the present invention provides a second sensor abnormality detecting circuit for a sensor having a first output terminal generating a first output voltage and a second output terminal generating a second output voltage, the first output voltage and the second output voltage varying in mutually opposed positive and negative directions in response to a sensed physical quantity by the same voltage amount with respect to a predetermined equilibrium voltage V0.
The second sensor abnormality detecting circuit comprises a reference voltage generating circuit for generating a reference voltage substantially identical with the equilibrium voltage. An operational amplifier has one input terminal receiving the reference voltage generated from the reference voltage generating circuit. A first differential amplifier has a non-inverting input terminal receiving the first output voltage of the sensor and an inverting input terminal receiving the reference voltage generated from the reference voltage generating circuit. A second differential amplifier has a non-inverting input terminal receiving the second output voltage of the sensor and an inverting input terminal receiving the reference voltage generated from the reference voltage generating circuit. A first resistor has one end receiving an output voltage of the first differential amplifier and the other end connected to the other input terminal of the operational amplifier. A second resistor has one end receiving an output voltage of the second differential amplifier and the other end connected to the other input terminal of the operational amplifier. The second resistor has the same resistance as that of the first resistor. A third resistor is connected between an output terminal of the operational amplifier and the other input terminal of the operational amplifier. And, a judging circuit generates an abnormal signal notifying an occurrence of sensor abnormality when an output voltage of the operational amplifier is outside a predetermined normal voltage range.
In other words, the second sensor abnormality detecting circuit provides the first and second differential amplifiers instead of using the first and second buffers.
It is now assumed, in the second sensor abnormality detecting circuit, that Y represents an amplification factor (i.e., amplification degree) of the first and second differential amplifiers. An output voltage V1S of the first differential amplifier can be defined by the following formula 2-3, while an output voltage V2S of the second differential amplifier can be defined by the following formula 2-4.
V1S=Yxc2x7(V1xe2x88x92VE)+VExe2x80x83xe2x80x83(2-3)
V2S=Yxc2x7(V2xe2x88x92VE)+VExe2x80x83xe2x80x83(2-4)
Thus, the formula 2-1 expressing the output voltage VOUT of the operational amplifier can be replaced by the following formula 2-5.
VOUTxe2x88x92Xxc2x7Y{(V1xe2x88x92VE)+(V2xe2x88x92VE)}+VExe2x80x83xe2x80x83(2-5)
As understood from the formula 2-5, according to the second sensor abnormality detecting circuit, when the balance of sensor output voltages V1 and V2 are lost, the output voltage VOUT of the operational amplifier largely deviates in either a positive or a negative direction from the reference voltage VE.
Accordingly, it becomes possible to accurately detect the sensor abnormality. Although the operational amplifier is generally not free from an offset voltage, the operational amplifier can operate at a region where the influence of the offset voltage is sufficiently small. The sensor abnormality detecting accuracy can be improved.
The first and second differential amplifiers can perform the roles similar to those of the above-described first and second buffers. Thus, it becomes possible to prevent the current from flowing excessively from the sensor output terminals into the circuit portion consisting of the operational amplifier and. the first to third resistors.
Furthermore, in the above first and second sensor abnormality detecting circuits, it is preferable that the judging circuit generates the abnormal signal when the output voltage VouT of the operational amplifier is higher than a first criterial voltage (VE+xcex1) which is higher than the reference voltage VE generated from the reference voltage generating circuit by a predetermined voltage xcex1, and the judging circuit generates the abnormal signal when the output voltage VOUT of the operational amplifier is lower than a second criterial voltage (VExe2x88x92xcex2) which is lower than the reference voltage VE generated from the reference voltage generating circuit by a predetermined voltage xcex2.
More specifically, a criterial voltage generating circuit is provided for generating the first criterial voltage higher than the reference voltage VE by the predetermined voltage a and for generating the second criterial voltage lower than the reference voltage VE by the predetermined voltage xcex2. The first criterial voltage and the second criterial voltage thus produced from the criterial voltage generating circuit are supplied to the judging circuit. The judging circuit is arranged to generate the abnormal signal when the output voltage VOUT of the operational amplifier is higher than a higher criterial voltage (i.e., the first criterial voltage) as well as when the output voltage VOUT of the operational amplifier is lower than a lower criterial voltage (i.e., the second criterial voltage). Although it is preferable to equalize the predetermined voltage xcex1 with the predetermined voltage xcex2, it is alternatively possible to differentiate the values of xcex1 and xcex2.
In the case of the sensor abnormality detecting circuit comprising the first to third buffers, the term of xe2x80x9c+VExe2x80x9d in the above-described formulas 2-1 and 2-2 is replaced by xe2x80x9c+(VE+Vsf)xe2x80x9d and the output voltage VOUT of the operational amplifier is regarded as a voltage varying with reference to the reference level of xe2x80x9cVE+Vsf xe2x80x9d.
Accordingly, it is effective to arrange the sensor abnormality detecting circuit to further comprise a fourth buffer for shifting the first criterial voltage generated from the criterial voltage generating circuit by the specific voltage Vsf identical with that of the first to third buffers and supplying a shifted first criterial voltage to the judging circuit, and a fifth buffer for shifting the second criterial voltage generated from the criterial voltage generating circuit by the specific voltage Vsf and supplying a shifted second criterial voltage to the judging circuit, in addition to the above-described criterial voltage generating circuit for generating the first criterial voltage and the second criterial voltage. The judging circuit is arranged to generate the abnormal signal when the output voltage VOUT of the operational amplifier is higher than the voltage (i.e., first criterial voltage +Vsf) supplied from the fourth buffer as well as when the output voltage VOUT of the operational amplifier is lower than the voltage (i.e., second criterial voltage +Vsf) supplied from the fifth buffer.
According to this arrangement, not only the output voltage VOUT of the operational amplifier but also the normal voltage range used for the abnormality judgement are shifted by the specific voltage Vsf Thus, the abnormality judgement can be performed without re-setting the first and second criterial voltages.
Furthermore, in the above first and second abnormality judging circuits, it is desirable that the sensor comprises four gauge resistors connected in a loop pattern so as to provide four connecting terminals of the gauge resistors, each of the gage resistors having a resistance varying in response to a deformation, a power voltage is applied to two opposed connecting terminals of the gauge resistors, and the rest of the connecting terminals of the gauge resistors serve as the first and second output terminals.
According to this arrangement, by using a compact circuit arrangement, it becomes possible to promptly and accurately detect the abnormality of the pressure sensor having four gauge resistors. Furthermore, according to this kind of pressure sensor, a difference between each of the output voltage V1 and V2 and the equilibrium voltage V0 is small. In this respect, using the above second sensor abnormality detecting circuit is effective.
When the sensor of the present invention is a pressure sensor, it is desirable that the reference voltage generating circuit comprises at least two resistors for dividing the power voltage to generate the reference voltage.
For example, the reference voltage generating circuit can be constituted by two resistors dividing the power voltage. In this case, the connecting point of two resistors is determined so as to generate a desired reference voltage.
The number of the resistors dividing the power voltage can be increased to three or more. In other words, the number of the voltage-dividing resistors can be arbitrary selected as far as the reference voltage is produced at a connecting point of the resistors.
According to this arrangement, even when the actual equilibrium voltage of the sensor is changed in response to a variation or fluctuation of the power voltage, the reference voltage can follow such a change. Thus, the abnormality detection of the pressure sensor can be accurately performed irrespective of the variation or fluctuation of the power voltage.
Furthermore, the present invention provides a physical quantity detecting apparatus associated with a sensor having a first output terminal generating a first output voltage and a second output terminal generating a second output voltage, the first output voltage and the second output voltage varying in mutually opposed positive and negative directions in response to a sensed physical quantity by the same voltage amount with respect to a predetermined equilibrium voltage. This physical quantity detecting apparatus has a physical quantity output terminal for producing a sensing signal representing the sensed physical quantity based on the first output voltage of the sensor and the second output voltage of the sensor.
Especially, the physical quantity detecting apparatus of the present invention comprises the above first or second abnormality detecting circuit for detecting a sensor abnormality. And, an abnormal signal notifying an occurrence of sensor abnormality is produced from the physical quantity output terminal instead of outputting the sensing signal when the sensor abnormality detecting circuit produces a signal indicating sensor abnormality.
According to this physical quantity detecting apparatus, when the operation of the sensor is normal, the physical quantity output terminal outputs the sensing signal representing the sensed physical quantity. Meanwhile, when the operation of the sensor is abnormal, the physical quantity output terminal outputs the abnormal signal notifying an occurrence of sensor abnormality. Accordingly, an electronic control apparatus or other apparatus which processes the sensing signal received from the physical quantity detecting apparatus can immediately know the occurrence of sensor abnormality upon receiving the abnormality signal produced from the physical quantity output terminal. There is no necessity of providing a special signal line separately.
Furthermore, the present invention has an object to provide a physical quantity detecting sensor capable of accurately detecting abnormality of the sensor.
To accomplish this and other related objects, the present invention provides a physical quantity detecting sensor comprising four gauge resistors each having a resistance varying in response to a sensed physical quantity, so that the four gauge resistors forming a bridge circuit. In this physical quantity detecting sensor, the gauge resistors constituting the bridge circuit are separate gauge resistors. A sensor output is produced based on a voltage difference between two midpoints of the bridge circuit. An inspection output is produced based on a voltage difference between a pair of intermediate terminals selected from intermediate terminals of the separate gauge resisters. The selected pair of intermediate terminals has the same voltage level in a condition where no physical quantity is applied on the sensor. And, adjusting means is connected to the selected pair of intermediate terminals for adjusting an error component of the inspection output.
In this manner, the physical quantity detecting sensor of the present invention includes the adjusting means for adjusting the error component of the inspection output, so that the adjusting means is connected to the selected pair of intermediate terminals having the same voltage level in a condition where no physical quantity is applied on the sensor. Thus, it becomes possible to adjust the sensitivity and an offset amount of the sensor output as well as a temperature offset amount, thereby reducing the error component even if the inspection output has such an error component. Hence, the abnormality detection can be accurately performed.
In this case, it is preferable that an amplification circuit is connected to the selected pair of intermediate terminals, and the adjusting means adjusts an output of the amplification circuit.
Furthermore, it is preferable that the adjusting means is a voltage-follower circuit, and an output voltage level of the amplification circuit is raised by an output of the voltage-follower circuit so as to adjust the error component of the inspection output.
For example, the voltage-follower circuit has a non-inverting input terminal receiving a reference voltage. The reference voltage is supplied from a power voltage based on a voltage division by first and second resistors. And, a resistance value of at least one of the first and second resistors is adjustable by trimming.
Furthermore, the present invention has an object to provide a pressure sensor having a practical arrangement for accurately detecting a sensor failure when an output of a bridge circuit is changed due to the failure.
To accomplish this and other related objects, the present invention provides a fifth pressure sensor comprising a semiconductor substrate having first and second diaphragm portions, a pressure detecting circuit provided on the first diaphragm portion for outputting an electric signal responsive to a pressure applied on the first diaphragm portion, a failure detecting circuit provided on the second diaphragm portion for outputting an electric signal responsive to the pressure applied on the second diaphragm portion, the failure detecting circuit having a sensitivity higher than that of the pressure detecting circuit, and failure judging means for performing a failure judgement of the pressure detecting circuit based on output signals of the pressure detecting circuit and the failure detecting circuit.
In this manner, by using the output signals of the pressure detecting circuit and the failure detecting circuit, it becomes possible to accurately detect the sensor failure when an output of the pressure detecting circuit is changed due to the failure. Furthermore, using the failure detecting circuit having the sensitivity higher than that of the pressure detecting circuit makes it possible to promptly detect the failure or deterioration (breakage etc) of the diaphragm portion prior to the pressure detecting circuit. The sensor failure detection becomes highly accurate. The reliability of the sensor is improved, and safety against the failure can be ensured.
Furthermore, it is preferable that an area of the second diaphragm portion is larger than an area of the first diaphragm portion. With this arrangement, the failure detecting circuit can have a sensitivity higher than that of the pressure detecting circuit. Furthermore, it is preferable that a thickness of the second diaphragm portion is smaller than a thickness of the first diaphragm portion. With this arrangement, the failure detecting circuit can have a sensitivity higher than that of the pressure detecting circuit.
Furthermore, it is preferable that the pressure detecting circuit and the failure detecting circuit are bridge circuits each consisting of a plurality of gauge resistors. Furthermore, the gauge resistors can be formed by difflused resistors or by thin-film resistors.
Furthermore, the failure detecting circuit can be provided on the semiconductor substrate having the diaphragm portion.
Furthermore, the present invention has an object to provide a dynamic quantity detecting sensor capable of detecting abnormality of the sensor and also capable of outputting a sensor signal responsive to a sensed dynamic quantity during an inspection of the sensor.
Furthermore, the present invention has an object to provide a dynamic quantity detecting sensor capable of detecting abnormality without using a redundant circuit arrangement.
To accomplish the above and other related objects, the present invention provides a dynamic quantity detecting sensor comprising a sensing portion having sensitivity varying in response to an applied voltage or an applied current, a signal processing circuit for processing an output of the sensing portion to generate an output signal representing the output of the sensing portion, a first sample hold circuit for holding an output signal of the signal processing circuit, an operational processing circuit for processing an output signal of the sample hold circuit responsive to a first impressed voltage or a first impressed current applied to the sensing portion as well as an output of the signal processing circuit responsive to a second impressed voltage or a second impressed current applied to the sensing portion, and a judging circuit for performing an abnormality detection based on the processing result of the operational processing circuit.
With this arrangement, the impressed voltage or the impressed current is differentiated for the dynamic quantity detection and for the diagnosis. The first sample hold circuit holds an output of the signal processing circuit during the dynamic quantity detection. An output of the signal processing circuit during the diagnosis is obtained. Then, abnormality detection is performed by checking whether or not the relationship between the output of the first sample hold circuit and the output of the signal processing circuit during the diagnosis satisfies a predetermined relationship. Accordingly, the abnormality of the dynamic quantity detecting sensor can be detected without using a redundant circuit arrangement.
The first sample hold circuit holds an output of the signal processing circuit. Thus, the first sample hold circuit can output a pressure signal representing an applied pressure even when the sensor is in a diagnosis mode.
More specifically, it is preferable that the operational processing circuit performs calculation based on the following formula 5-1.
V2=(axc3x97V1xe2x88x92(axe2x88x921)xc3x97VO)xe2x80x83xe2x80x83(5-1)
where V1 represents the output signal of the sample hold circuit responsive to the first impressed voltage or the first impressed current applied to the sensing portion, V2 represents the output signal of the signal processing circuit responsive to the second impressed voltage or the second impressed current applied to the sensing portion, xe2x80x9caxe2x80x9d represents the ratio of the second impressed voltage or the second impressed current to the first impressed voltage or the first impressed current, and VO represents an offset voltage of the output of the sensing portion.
According to a preferred embodiment of the present invention, it is preferable that the signal processing circuit generates the output signal of a predetermined range during a dynamic quantity detection, and the judging circuit converts the output signal of the signal processing circuit into a specific output signal when an abnormality is detected based on the output signals of the operational processing circuit, the specific output signal having a signal level different from the predetermined range of the output signal of the signal processing circuit generated during the dynamic quantity detection.
In this manner, by outputting the specific output signal having a signal level different from the predetermined range of the output signal generated during the dynamic quantity detection, it becomes possible to detect the abnormality of the sensor output.
Furthermore, it is preferable that the offset voltage is set to be outside the predetermined range of the output signal generated from the signal processing circuit during the dynamic quantity detection. According to this arrangement, the output voltages V1 and V2 are mutually discriminative in this range. Thus, the abnormality detection of the sensor can be accurately performed based on the above-described formula.
Furthermore, it is preferable that the dynamic quantity detecting sensor further comprises a second sample hold circuit for holding an output of the judging circuit. Using the second sample hold circuit for holding the output of the judging circuit makes it possible to notify an occurrence of sensor abnormality throughout the holding term of the output of the judging circuit.
Furthermore, it is preferable that the dynamic quantity detecting sensor further comprises a timing circuit for generating a timing signal so as to perform a switching operation between the first impressed voltage or the first impressed current and the second impressed voltage or the second impressed current based on the timing signal, and the first sample hold circuit and the second sample hold circuit can operate based on the timing signal.
More specifically, it is preferable that the timing signal generated from the timing circuit causes the first sample hold circuit to hold the output signal of the signal processing circuit, and then causes the switching operation between the first impressed voltage or the first impressed current and the second impressed voltage or the second impressed current, and finally causes the second sample hold circuit to hold the output signal of the judging circuit.
Furthermore, the present invention has an object to provide an effective layout of piezoelectric resistors for a pressure detecting apparatus comprising a pressure receiving diaphragm, a plurality of piezoelectric resistors formed on a surface of the diaphragm each having a resistance value varying in accordance with a distortion of the diaphragm, and a plurality of bridge circuits each constituted by the plurality of piezoelectric resistors, which is capable of performing the failure diagnosis.
To accomplish the above and other related objects, the present invention provides a pressure detecting apparatus comprising a diaphragm for receiving a pressure, a plurality of piezoelectric resistors formed on a surface of the diaphragm, each of the plurality of piezoelectric resistors having a resistance value varying in accordance with a distortion of the diaphragm, and a sensing circuit comprising a first bridge circuit and a second bridge circuit each constituted by the plurality of piezoelectric resistors. The first bridge circuit generates a first bridge output representing the distortion of the diaphragm caused when the pressure is applied on the diaphragm. The plurality of piezoelectric resistors of the second bridge circuit are connected in a predetermined relationship so as to generate a second bridge output which does not change in response to the distortion of the diaphragm.
According to the present invention, the first bridge circuit performs the pressure detection. Meanwhile, the second bridge circuit is not influenced by the pressure detection because its bridge output does not change in response to the distortion of the diaphragm. The second bridge circuit is not influenced by the dislocation caused in the arrangement of piezoelectric resistors.
The second bridge circuit is constituted by the piezoelectric resistors whose resistance values vary in accordance with a distortion of the diaphragm. The output of the second bridge circuit changes when the diaphragm is broken or when the resistance value of the piezoelectric resistor changes. Thus, the sensor failure can be detected by checking the change of bridge output of the second bridge circuit.
In this manner, the present invention provides a pressure detecting apparatus capable of performing a sensor failure diagnosis by providing the second bridge circuit. The freedom of layout of piezoelectric resistors in the second bridge circuit can be improved. Consequently, it becomes possible to provide an effective arrangement for the piezoelectric resistors.
Furthermore, it is preferable that the surface of the diaphragm is a (100) surface of a silicon semiconductor substrate, and the piezoelectric resistors are formed on the (100) surface in the first and second bridge circuits.
Using the (100) surface of the silicon semiconductor substrate as the surface of the diaphragm is preferable in that the piezoelectric resistors of the first and second bridge circuits can be easily disposed by utilizing two  less than 110 greater than  crystal axes existing on the (100) surface.
Furthermore, it is preferable that the piezoelectric resistors constituting the first bridge circuit and the piezoelectric resistors constituting the second bridge circuit are disposed concentrically about the center of the diaphragm. This arrangement is advantageous in that wiring connection for each bridge circuit can be easily done.
Moreover, it is preferable that a pair of opposed piezoelectric resistors constituting part of the first bridge circuit cause a voltage change along a circumferential direction of a concentric circle having a center identical with the center of the diaphragm, while the other pair of opposed piezoelectric resistors constituting the rest of the first bridge circuit cause a voltage change along a radial direction of this concentric circle, and all of the piezoelectric resistors constituting the second bridge circuit cause a voltage change along a radial direction of a corresponding concentric circle.
Moreover, the present invention has an object to provide a pressure sensor capable of surely detecting a sensor failure without using a specific failure detecting bridge circuit or without using specific gauge resistors.
To accomplish the above and other related objects, the present invention provides a sixth pressure sensor having a pressure sensing circuit with a plurality of gauge resistors and a plurality of output terminals. The sixth pressure sensor comprises a memory means for storing a relationship of respective outputs of at least two output terminals arbitrarily selected from the plurality of output terminals, and a failure judging means for performing a failure judgement of the pressure sensing circuit by checking whether or not respective outputs of the selected output terminals measured at an arbitrary pressure point satisfy the relationship stored in the memory means.
With this arrangement, it becomes possible to monitor the variation of an output of each output terminal in the pressure sensing circuit and accurately obtain the relationship ofrespective terminal outputs, thereby realizing a highly reliable sensor failure judgement.
According to a preferred embodiment of the present invention, it is preferable that the pressure sensing circuit is a bridge circuit and the failure judgement of the pressure sensing circuit is performed based on voltage outputs of two midpoint terminals of the bridge circuit.
Furthermore, it is preferable that the failure judgement of the pressure sensing circuit is performed by checking whether or not the output of the second output terminal is within a predetermined range with respect to the output of the first output terminal, the predetermined range being determined based on the relationship stored in the memory means. This predetermined range can be arbitrarily set by considering a possible manufacturing error of the pressure sensor or the detecting accuracy.
Furthermore, the present invention has an object to provide a pressure sensor which is capable of detecting an abnormality in its output sensitivity.
To this end, the present invention provides a seventh pressure sensor comprises a diaphragm deformable in response to a pressure applied thereon, and a plurality of gauge resistors generating an electric signal representing the applied pressure based on a distortion of the diaphragm. The seventh pressure sensor includes at least six gauge resistors each having a resistance value varying in accordance with the applied pressure. The six gauge resistors consist of incremental gauge resistors each having a resistance value increasing in accordance with the applied pressure and the decremental gauge resistors each having a resistance value decreasing in accordance with the applied pressure. The electric signal representing the applied pressure is produced based on a voltage difference between two predetermined points of a plurality of connecting points of the six gauge resistors, and a sensor failure is detected based on a voltage difference between two another points of the connecting points.
According to this arrangement, among the six gauge resistors having a resistance value varying in response to an applied pressure, at least four gauge resistors are used for constituting a bridge circuit. The electric signal representing an applied pressure can be produced based on a voltage difference between the predetermined connecting points. Thus, the applied pressure can be detected.
Furthermore, providing at least six gauge resistors electrically connected to each other makes it possible to select two connecting points whose voltage levels do not vary in response to an applied pressure as far as all of the gauge registers are normal. The two selected connecting points are other than the two connecting points used for detecting the applied pressure.
If any failure occurs in a gauge resistor during the operation of the sensor, the voltage difference between two selected connecting points causes a variation and can be detected as a failure of the sensor. Accordingly, it becomes possible to provide a pressure sensor capable of detecting an abnormality in its output sensitivity.
Furthermore, the gauge resistors includes at least six resistors each having a resistance value varying in accordance with the applied pressure, It is preferable that the first gauge resistor is connected to the second gauge resistor at the first connecting point. The second gauge resistor is connected to the third gauge resistor at the second connecting point. The third gauge resistor is connected to the fourth gauge resistor at the third connecting point. The fourth gauge resistor is connected to the fifth gauge resistor at the fourth connecting point. The fifth gauge resistor is connected to the sixth gauge resistor at the fifth connecting point. And, the sixth gauge resistor is connected to the first gauge resistor at the sixth connecting point.
The first and fifth gauge resistors cause resistance changes in the same direction when the pressure is applied on the diaphragm, while the second and sixth gauge resistors cause resistance changes in the opposed direction when the pressure is applied on the diaphragm. The third gauge resistor and the fourth gauge resistor cause resistance changes in the same direction when the pressure is applied on the diaphragm.
Furthermore, the electric signal representing the applied pressure is produced based on the voltage difference between the first connecting point and the fifth connecting point caused when a voltage or current is supplied between the third connecting point and the sixth connecting point, while the sensor failure is detected based on the voltage difference between the second connecting point and the fourth connecting point.
According to the present invention having the above-described characteristic arrangement, the first, second, fifth, and sixth gauge resistors cooperatively constitutes a bridge circuit. The voltage difference between the first connecting point and the fifth connecting point is proportional the applied pressure. Thus, the applied pressure is detectable based on the electric signal caused between the the first connecting point and the fifth connecting point.
The third gauge resistor and the fourth gauge resistors cause the resistance change in the same direction in response to the applied pressure. When all of the gauge resistors are normal, no adverse influence is given to the voltage difference between the first connecting point and the fifth connecting point. The voltage difference between the second connecting point and the forth connecting point does not change.
If any one of the first to sixth gauge resistors is failed, the voltage difference between the second connecting point and the fourth connecting point will be changed. This change can be detected as a failure signal. Accordingly, the present invention provides a pressure sensor capable of detecting an abnormality in the output sensitivity.
Furthermore, it is desirable that the third and fourth gauge resistors and the first and fifth gauge resistors cause the resistance changes in the same direction.